Reciprocating internal combustion engines having a balancer device are known. In such a balancer device, a balancing weight corresponding to about half of a total reciprocating mass of the reciprocating piston, the connecting rod and so on is mounted on the crankshaft. A balancing weight of the same weight is mounted on a balancer shaft. The balancer shaft is rotated at the same speed as and in a direction opposite to the crankshaft to decrease or eliminate imbalance in rotational inertia forces produced by the aforesaid total reciprocating mass during the reciprocating motion. However, when the balancer device is driven by a gear drive method, gear teeth striking noises occur due to backlash between gears in each meshed portion. Particularly during idling operation of the engine, the gear teeth striking noises become loud.
Means for preventing or reducing the gear teeth striking noises in the balancer drive system referred to above are known. In known means, a portion of gears for the transfer of rotational force from the crankshaft to the balancer shaft, is provided with elastic members, such as rubber members, interposed as dampers between the driving side and the driven side, and vibrations or the like transmitted from the crankshaft to the balancer shaft are damped to effect a smooth transfer of torque (see, for example, Patent Document 1). In this case, a measure for preventing the occurrence of an error at the time of assembling gears has been taken such as making the arrangement of the elastic members asymmetric or setting the number of gear teeth to an even number (see, for example, Patent Document 2).
[Patent Document 1]
JP 60-192145 A (FIG. 5)
[Patent Document 2]
JP 07-71532 A (FIG. 2, Reference numeral 11)